Software

Rename the folder - replace dash with underscore (Adafruit_PN532)
Place the Adafruit_PN532 library folder your <arduinosketchfolder>/libraries/ folder. You may need to create the libraries subfolder if its your first library. Restart the IDE.

You should now be able to select File > Examples > Adafruit_NFCShield_I2C > readMifare sketch. Upload the sketch to your Arduino with the shield plugged in, open the serial monitor.